1. Field of the Invention
The present invention relates to the field of lumber sorters, and more particularly to such sorters having flexible slings with releasable ends to form cradles for receiving the sorted lumber.
2. Description of the Prior Art
Like many businesses, the lumber industry has become highly mechanized. Machines convert forest timber to building lumber with minimal human assistance. The machines receive raw logs which are processed and cut to produce building lumber and a variety of other useful products. When this final process is complete, the lumber must be sorted and packaged for delivery to users.
The modern sling sorter system for sorting lumber, such as the Harvey Engineering and Manufacturing (HEMCO) inline planermill and green lumber sorting system, is common in the lumber industry and performs the lumber sorting operation rapidly. A conveyor receives each board of lumber of assorted lengths. As the board is cut and trimmed to the particular specifications, a computer records the board's position on the conveyor.
The conveyor then moves the cut lumber along a plurality of parallel rails. The rails are divided into segments so that a set of segments may temporarily swing upward, creating an opening in the parallel rails. The segments are controlled by the computer. When a board of particular specifications reaches a point directly above a certain location on the rails, the rail segments are controlled by the computer. When a board of particular specifications reaches a point directly above a certain location on the rails, the rail segments automatically swing upward, and the board drops through the opening. The lumber is sorted by dropping all lumber of the same specification through the same opening, or additional bays, if required.
Beneath each opening are, typically, from three to five flexible slings. The slings hang parallel to the rails across the opening, and are usually made of tough webbing. As the boards fall through the opening, they are received by lumber receiving cradles defined by the plurality of laterally spaced flexible slings.
One end of each sling is securely attached to a sling spool or reel mounted on a power-operated drive shaft. The other end of each sling features a D-ring permanently attached by inserting the sling webbing through the D-ring and sewing the sling webbing to itself. The D-ring, as the name indicates, is typically shaped like the letter "D" or is approximately triangular in shape. The end of the sling webbing loops over the base of the triangle and is securely sewn to itself. One such D-ring is disclosed in Applicant's U.S. Pat. No. 5,123,690. Applicant hereby incorporates by reference U.S. Pat. No. 5,123,690 in its entirety.
The D-ring releasably attaches to a pivoting hook which is permanently connected to the sorter frame. Each sling spool contains several wraps of a flexible sling of suitable length. The power-operated drive shaft allows the plurality of slings in each bay to pay out or take up the slings as required. As the sling cradle fills with lumber, the sling spool is unwound so as to deliver more sling so that the sling cradle remains essentially full without overloading. This feature minimizes damage to the boards by reducing the falling distance of the newly sorted lumber onto the lumber already being supported in the sling cradle.
The lumber collected in the sling cradle is ultimately unloaded onto an underlying conveyor. The unloading is performed by paying out the slings until the lumber is resting on the underlying conveyor. With the slings relaxed, the hook is withdrawn from the D-ring, thus permitting the D-ring and free end of each sling to fall to the floor surface. After the free ends of the slings have been released, the power-operated drive shaft takes up the slings onto the sling spools. The sling webbing passes through a retriever assembly attached to the sorter frame and positioned below the sling spool. The sling spool retrieves the sling through the retriever assembly until the D-ring is firmly received in a slot at the end of the retriever assembly. Continued rotation of the sling spool causes the retriever assembly with the received D-ring to pivot upwards approximately 90.degree. so that it extends substantially horizontally across the bay opening.
The lumber sorter includes a mechanism for recapturing the D-ring and free end of the slings in the retriever assembly to reform the lumber cradle. The hook is pivotably connected to the sorter frame and made to extend towards the horizontally positioned retriever assembly. As the retriever assembly pivots to the horizontal position the hook catches the D-ring at the end of the retriever assembly. The hook is remotely controlled, typically by hydraulics and/or air. By engaging the D-ring with the hook, the bay is now ready to receive the next load of lumber. The first sorted boards fall gently onto the retriever assembly and/or hook. As the sorted lumber falls into the bay, the hook is rotated in a slight downwardly direction and the power-operated drive shaft rotates the sling spool to pay out a sufficient length of sling to permit the retriever assembly to rotate to a substantially vertical hanging position as the sling cradles fill with the sorted lumber.
Sling-type lumber sorters of the above-described general type are disclosed in U.S. Pat. Nos. 3,776,379, 4,098,407, and 4,104,156.
One problem with the above-described sling-type lumber sorters results from the fact that the plurality of slings in each bay are uniformly spaced from one another and the lumber being sorted in the bay may not have a length sufficient to be supported by one or more of the "uneven end" slings. As the lumber is initially transported along the set of parallel rails, all of the boards of various lengths have an aligned end which is referred to as the "even end." The other end of the boards is referred to as the "uneven end." Typically, each bay has 4-6 slings spaced approximately 3-4' from one another which thus can handle boards having a length of up to 24' or greater. However, this same bay may be required to receive boards having a length of only 10' in which case only the 2 or 3 slings nearest the even end (even end slings) receive the lumber. The problem arises with the flexible slings which are not presently receiving the lumber (uneven end slings) in the bay and which are expected to cleanly pay out from the sling spool as the power-operated drive shaft rotates all of the sling spools in that bay. The absence of weight on these non-loaded uneven end slings results in many problems, such as these slings becoming twisted, becoming slack on the sling spool, slipping off of the sling spool and wrapping around the drive shaft, or becoming slack on the sling spool and then doubling up on itself. Oftentimes, the uneven end slings have a life expectancy of only 1/3 that of even end slings. Occasionally, the uneven end slings may last only 15% of the life of the even end slings. Thus, maintenance of uneven end slings is a constant problem requiring inspection. The operator's safety is jeopardized by poorly maintained and inspected slings. The premature wear of the slings reduces the useful life of the sling. To prevent a failure, the sling must be periodically replaced. Replacement of a damaged sling involves shutting down the entire sorter apparatus. The owner pays for the materials and labor for the replacement, and also experiences a reduced sorter system efficiency due to the temporary shut down of the entire sorter apparatus. Most importantly, failure to routinely maintain and inspect the slings subjects human lives to increased risks.
The problem mentioned above may also result in irreparably damaging the sling spool on the drive shaft. Presently, replacement of the sling spool requires removal of the drive shaft and the associated drive mechanism. Typically, this requires the lumber sorter apparatus to be shut down for several hours. Thus, oftentimes a badly damaged sling spool will not be replaced until absolutely necessary even though additional damage may be resulting to the sling. Additionally, the sling spool is presently held in place on the drive shaft with a set screw which bears against the drive shaft. If the sling spool slips longitudinally on the drive shaft, vertical misalignment of the sling spool with the retriever assembly results. The misalignment causes both premature wear on the sling and the sling spool.
Frequently, slings become twisted below the retriever assembly and cause jamming at the retriever assembly when retrieving the slings onto the sling spools. The operator typically walks to the twisted sling to remove the twist. However, in order to get to the twisted sling the operator may walk beneath suspended lumber in adjacent bays. Failure of a sling in an adjacent bay would result in falling lumber inflicting serious bodily harm to the operator below.
Another problem associated with the sling sorter system described above is with the retrieval of the D-ring in the slot of the retriever assembly. Occasionally, the D-ring rotates relative to the length of the sling webbing at the point of attachment which results in the D-ring not being received in the slot of the retriever assembly upon retrieval. This additionally prevents the hook from catching the D-ring and forming the cradle for the next load of sorted lumber. The operator has to stop the operation until the D-ring is properly received in the retriever assembly.
The sling sorter system described above is more commonly used in the softwood industry as opposed to the hardwood or precious wood industry. The primary reason for this is the higher cost of hardwood or precious wood lumber and the damage that may result to the boards as they are sorted by the sling sorter system. Hardwood lumber is more prone to damage or breakage as the lumber is dropped from the upper rails to the underlying stack of lumber or cradles.
It is desirable to have a drop sling lumber sorter apparatus which increases the useful life expectancy of uneven end slings and minimizes the amount of down time required to maintain and repair the lumber sorter apparatus. It is also desirable to improve the safety of the operators during operation of the lumber sorter apparatus. It is also desirable to improve the lumber sorter apparatus to reduce the amount of damage to the lumber as it is being sorted and also to make the lumber sorter apparatus more suitable for use in the hardwood or precious wood industry.